This is the best amateur refractor I have looked thru. Now what that does is exclude all large refractors over 6" since 6" is the largest I have been able to use.

Nothwithstanding the aperture limitation this scope presented outstanding views of the disc of Neptune with some detail. I have not seen any reflector, SCT including our Chicago Astronomical Society's 14 MEADE LX200 on a Paramount ME produce views anywhere close to this wonderful scope.

I owned a 5" f/12 Superplanetary which, presumably, would have slighly less color than a 6" f/12 Superplanetary. Nevertheless, I found it to be less well color corrected than an FS-128 (but considerably better corrected than a 5" f/15 D&G achro as would be expected).

These two AP scopes hold a special interest for me. I placed an order for one in 1985. Then kid #1 was born and our family moved to a new house. Had to cancel the order. AP refunded my deposit no questions asked. The most amazing thing was when I placed another order 20 years later they still had my information in their data base! In a world with so much shoddy customer service and shoddy behavior in general, it's nice to deal with a company that has integrity. Hard to place a price on that.

I have the 5" AP superplanetary. I think the colour correction in focus is comparable if not equal to my FS-102. I was tempted for the 6" AP SP and also the D&G 6" f12 recently posted but had decided 5" f/12 was my limit for storage, lifting, mounting and transporting.

The 6" f/8 would I think fail even Roland Christen's definition of "APO today, though at the time it was sold, it was considered an APO (1/8000th of the focal lenght spacing).

Anyway, the 6" f/8 is not color free. The only ray trace for a similar design I have is for an 8" f/10 Christen Immersion Triplet. In this design, the red, green, and blue are well corrected, but the violet spread is very defocused (about 30mm at the focal plane). This is so diffuse that it would be difficult to see unless the star is very bright (Sirius or Vega). This is consistent with the 6" f/8. The violet is defocused over a very wide area and unless the star is very bright, you can't see it.

I am sure the correction is not as good as the Superplanetary, but it is excellent in red, green, and blue. When cooled, stars appear to be color free, but again, bright stars will show a very faint but very large diffuse violet in the field. Barely detectable even on the brightest stars.

Optical quality though I would think could not be better than in the 6" f/8. I think Mr. Christen is perhaps a compulsive type incapable of letting something go out the door that is not made to standards that border on absolute perfection.

My 6" f/8 has the best optical of any telescope I have ever star tested. Flawless. Perfect breakout on the SA test, and optics that are as smooth as I have ever seen. I don't know for the life of my how the Superplanetary could be better than this because it is optically about as perfect as one could ask for. There is no meaningful improvement to be found beyound this level of quality. It would be a meaningless decimal place change on the Strehl report.

The last one on astromart tube only, sold for only 3500 IIRC. That corresponds well to 5k with a G11. A unitron guidescope and ap800 aren't worth $4000 (he is asking 7500 not 7000 my mistake) but good luck to the seller. If someone with deep pockets missed the ebay auction and decides suddenly he has to have a superplanetary (they don't come up.for sale all that often) it might sell for that. You can check feedback and see if he is flipping the 3500 dollar OTA for a Christmas bonus.